Preparation of phenanthrolines



United States Patent Oflice 3,426,026 Patented Feb. 4, 1969 3,426,026 PREPARATION OF PHENANTHROLINES Brian Colwell Ennis, Ripponlea, Victoria, and William Edgar Matthews, Armadale, Victoria, Australia, assignors to Monsanto Chemicals (Australia) Limited, West Footscray, Victoria, Australia, a company of Victoria No Drawing. Filed Aug. 17, 1964, Ser. No. 390,171 US. Cl. 260-288 9 Claims Int. Cl. C07d 39/14 This invention relates to a process for the preparation of alkyland aryl-substituted 1,10-phenanthrolines, the process of the invention providing high yield preparation of .a wide range of 1,10-phenanthrolines which are useful for various purposes.

Alkyl-substituted phenanthrolines have been prepared by the reaction of 8-aminoquinolines with p-vinyl ketones or li -vinyl aldehydes or their precursors in the presence of large amounts of strong mineral acids, together with an oxidizing agent such as o-nitrophenol, o-nitrobenzene sulfonic acid or arsenic acid. The yields are often low, rarely exceeding 20%; moreover, the large amounts of tarry by-products formed makes the purification of the phenanthroline very difficult.

We have now discovered that alkyland aryl-substituted 1,10-phenanthrolines can be prepared in high yield and without the formation of large amounts of tarry byproducts, thus simplying purification, by reacting a quino line selected from S-aminoquinolines and salts of 8- aminoquinolines, with a carbonyl component selected from fi-vinyl ketones and fl-vinyl aldehydes and precursors which generate such ketones and aldehydes under aqueous acidic conditions. Said fi-vinyl ketones and [Si-vinyl aldehydes have the structure,

wherein R, R and R are selected from hydrogen, alkyl and aryl groups. The process is practiced by heating said quinoline and said carbonyl component in a reaction medium consisting essentially of arsenic acid in a reaction stage conducted at a temperature up to about 130 C., and recovering the 1,10-phenanthroline from the reaction mixture. In the process of the invention, the arsenic acid reaction medium serves as solvent for the reactants and provides the acidic and oxidizing environment required for the reaction. Furthermore, the yield of phenanthroline is :much enhanced.

Quinolines used as a reactant in the process of the invention include S-aminoquinoline and the S-aminoquinolines substituted in any one or more of the 2-, 3-, 4-, 5- or fi-positions with alkyl or aryl groups, the 7- position remaining unsubstituted. The alkyl groups preferably have from 1 to 4 carbon atoms, and desirably there are up to two such groups. The aryl groups are preferably phenyl, tolyl or xylyl. Particularly useful quinolines include 8-arninoquinoline, 4-rnethyl-8-aminoquinoline, 2,4-dimethy1-8-aminoquinoline and 3,4-dimethyl-S-aminoquinoline. Acid addition salts of the quinolines which are used in the process of the invention include the salts of mineral acids, e.g., hydrochloride and sulfate. In some cases, an acid addition salt such as the hydrochloride may be preferred in providing acidic conditions for use in conjunction with precursors for generating the fi-vinyl aldehyde or fl-vinyl ketone component.

The fi-vinyl aldehydes used in the process of the invention preferably are those represented by the structural formula,

wherein R and R are selected from hydrogen, alkyl containing from 1 to 4 carbon atoms and phenyl. Examples of such B-vinyl aldehydes are acrolein, crotonaldehyde, tiglic aldehyde, a-methacrolein, u-ethyl-B-n-propylacrolein, u-ethylacrolein, a-butylacrolein and cinnamaldehyde. Since the reaction of the invention to form 1,10-phenanthrolines involves firstly the addition of the amino group of the quinoline component across the double bond of the carbonyl component, and since the carbonyl group of o e-unsaturated aldehydes tends to condense with aminoquinolines, which leads to the formation of unwanted side-products, there is often a definite yield advantage to be obtained by starting with a precursor of the /8-vinyl aldehyde (i.e., an aldehyde derivative in which the carbonyl group is protected and which readily generates the fi-vinyl aldehyde under the acidic conditions of the reaction). Precursors of B-vinyl aldehydes useful for carrying out the process of the invention can be represented by the structural formulas,

wherein X and X are selected from hydrogen and alkyl; wherein Z is selected from hydroxy, alkoxy, acetoxy and halogen; and wherein Y is selected from alkoxy, acetoxy and halogen. In these cases, the alkyl and alkoxy groups preferably contain from 1 to 4 carbon atoms and the halogen is preferably chlorine. Thus, in the case where it is desired to use acrolein as the El-vinyl aldehyde, there is preferentially used acrolein diethyl acetal or acrolein diacetate, and other such sources of acrolein include chloropropionaldehyde, B-hydroxypropionaldehyde, [3- alkoxypropionaldehydes and 1,l,3-trialkoxypropanes.

The ,B-vinyl ketones used in the process of the invention preferably are those represented by the structural formula,

o XCH=C-- wherein X and X are selected from hydrogen and alkyl groups containing from 1 to 4 carbon atoms; and wherein Q is selected from phenyl and alkyl groups containing from 1 to 4 carbon atoms. Examples of such ,B-vinyl ketones are methyl vinyl ketone, methyl isopropenyl ketone, ethyl isopropenyl ketone, phenyl propenyl ketone, pent-3- en-2-one and phenyl vinyl ketone. In the case of 8-vinyl ketones, there may be no particular advantage in using a precursor equivalent as in the case of the ,B-vinyl aldehydes. However, li-vinyl ketones are often prepared by condensing an aldehyde with a methylene group which is alpha to the carbonyl group of the ketone, followed by dehydration of the resultant fi-hydroxy ketone to the required fi-vinyl ketone. Thus, methyl isopropenyl ketone is commonly prepared by condensing formaldehyde with methyl ethyl ketone which gives l-hydroxy-2-methylbutan-3-one as intermediate, and this intermediate may be dehydrated by heating in the presence of a mineral acid catalyst to give methyl isopropenyl ketone. Accordingly, it is sometimes more convenient to use such a fi-vinyl ketone precursor as a reactant in the synthesis of 1,10- phenanthrolines in accordance with the invention, the desired ,8-vinyl ketone being generated in situ (i.e., methyl isopropenyl ketone may be so generated from the use of 1-hydroxy-2-methylbutan-3-one as the carbonyl component). Precursors of B-vinyl ketones useful for carrying out the process of the invention can be represented by the structural formulas,

wherein X and X are selected from hydrogen and alkyl; wherein Q is selected from alkyl and phenyl; wherein Z is selected from h-ydroxy, alkoxy, acetoxy and halogen; and wherein Y is selected from alkoxy, acetoxy and halogen. In these cases, the alkyl and alkoxy groups referably contain from 1 to 4 carbon atoms and the halogen is preferably chlorine. Examples of such precursors are lhydroxy-2-methylbutan-3-one, 4-hydroxybutan-2-one and fi-hydroxypropiophenone.

In carrying out the process of the invention, equimolar amounts of the quinoline component and the ,B-vinyl ketone or fi-vinyl aldehyde or precursor may be used. However, we prefer to operate the process with a l-50% molar excess of the stoichiometric amount of the ,B-vinyl ketone or [SE-vinyl aldehyde or precursor. In this way, virtually all of the quinoline component is utilized.

The arsenic acid reaction medium may be pure H AsO However, the usual commercial grade of arsenic acid containing 65% As O is satisfactory. The amount of arsenic acid used in the process of the invention, in constituting the reaction medium, should be such that the reaction mixture is fluid and capable of being stirred. In practice, not less than 1.5 mols/mol of quinoline component is employed, with a practical maximum amount of about mols/mol of quinoline component, the preferred amount being about 2.5 mols/mol of quinoline component.

Owing to the nature of the arsenic acid reaction medium, a solvent or diluent is not normally required in carrying out the process of the invention. However, a weak organic acid diluent, such as acetic acid, or an organic diluent, such as ketone, may be used if desired. Substantial amounts of water may be present in, or added to, the reaction mixture without adversely affecting the reaction, We have found, however, that the addition of substantial amounts of a reagent such as sulfuric acid, zinc chloride and aluminium chloride, which might be expected to aid the cyclization, often adversely affects the yield of phenanthroline, although small amounts have no marked effect. In the case where a zinc or aluminium salt is so present, the phenanthroline product can precipitate as the metal complex, which can be easily decomposed to the phenanthroline base by addition of caustic soda or the like.

In general, the process of the invention can be carried out by mixing together the S-aminoquinoline component, the B-vinyl aldehyde or li-vinyl ketone or precursor component, and the arsenic acid, and heating together at a temperature within the range of 130 C. until reaction is complete. We prefer to add the aldehyde or ketone or precursor component to a stirred mixture of the other two components, since this gives better control of the reaction. Thus, the aldehyde or ketone or precursor component may be added gradually to a mixture of the quinoline and arsenic acid which is refluxing at atmospheric pressure. Alternatively, the reaction components can be kept at a relatively low temperature, i.e., 2040 C., during the mixing or addition period, and when mixing or addition is complete, the temperature gradually raised to a temperature within the range of 50l30 C. to complete the reaction. The time allowed for the reaction is not particularly critical. We have found that from one to six hours at the reflux temperature is generally suflicient for the reaction to proceed to completion. When reaction is complete, the 1,l0-phenanthroline is recovered and purified by conventional procedures. In general, the excess of arsenic acid is partly neutralized with a base, such as caustic soda, and the precipitated non-basic or feebly basic impurities are removed. Further neutralization liberates the 1,10-phenanthroline, which is then isolated and purified, for example, by distillation or crystallization.

In an alternative procedure according to the invention, a p-quinolylarnino aldehyde or fl-quinolylamino ketone intermediate reaction product, which is obtained by contacting the quinoline component with a ,B-vinyl ketone or a fl-vinyl aldehyde or precursor in the presence of a weak organic acid catalyst at a temperature within the range of 20-40" C., is cyclized and dehydrogenated to the 1,10-phenanthroline in a final reaction stage by being heated to a temperature up to C. in a medium consisting essentially of arsenic acid. This procedure is conveniently carried out by allowing the quinoline component and the ,B-vinyl aldehyde or ,B-vinyl ketone or precursor component to react together in the presence of the weak organic acid catalyst to give the fl-quinolylamino aldehyde or fl-quinolylamino ketone intermediate reaction product; the intermediate product recovered and purified, for example, by distillation or crystallization; and the purified intermediate product then added gradually to a reaction medium consisting essentially of arsenic acid heated to a temperature up to 130 C., to effect cyclization and dehydrogenation to the 1,10-phenanthroline. At the end of the cyclization reaction, the 1,10-phenanthroline is isolated, for example, by neutralization of the arsenic acid, and purified by normal methods or by any special methods described in the literature.

Relatively large amounts of acetic acid may be used in preparing said fi-quinolylamino aldehyde or fi-quinolylamino ketone intermediate product, in this case the organic acid incidentally serving as a solvent for the reaction components; in other cases, it is possible to employ an inert diluent such as a saturated aliphatic ketone as a solvent, even though solvents are not normally required for such condensation reaction. A reaction time of three to four hours at room temperature (20 C.) is usually suflicient for the intermediate condensation reaction product to be formed in high yield; shorter times of reaction suffice at the higher temperature (40 C.). When an aldehyde or ketone precursor is used, as say a fi-hydroxy aldehyde or fi-hydroxy ketone, the reaction temperature and organic acid catalyst concentration should be increased to ensure that the required a,/3-unsaturated carbonyl compound is liberated.

The intermediate reaction product formed as described above need not be isolated before the cyclization step, in this caee the crude intermediate containing the excess of ,B-vinyl ketone or fl-vinyl aldehyde or precursor component being directly cyclized to the l,lO-phenanthroline by being added to the refluxing arsenic acid. Advantageous- 1y, an excess of the B-vinyl ketone or fl-vinyl aldehyde or precursor component (10% to 50% excess) is used in the preparation of such condensation product. A suitable addition time is 0.5 hour, after which the mixture is advantageously refluxed for a further one to two hours. Again, a large excess of arsenic acid is desirable, and it may be necessary to distill water from the mixture to maintain the reaction temperature. The 1,10-phenanthroline is recovered and purified, for example, by distillation or crystallization, as before.

3,426,026 5 6 The process of the invention is illustrated by the follow- EXAMPLE 3 mg non'hmltatws examples: Preparation of 3,4, 8-trimeflhyl-l,104phenanthroline EXAMPLE 1 A mixture of 3,4-dimethyl-8-aminoquinoline (8.6 g.),

methacrolein diacetate (10 g.) and acetic acid (10 ml.)

Pre aration of 3,4,7,8-tetra th 1-1,10- h thr l' p me y p enan me was heated to 90 C. for one hour. Arsenic acid (20 ml.)

A mixture of ily q was then added, and the mixture was refluxed for two g-, 0.058 mol) methyl lsopropenyl ketone (4.9 g., 0- hours. The solution was cooled and basified to a pH of mol) and glaclal acetlc acld was Stirred for one with sodium hydroxide solution. Oily by-products were hour at room temperature hhtll all the amine had removed, and basification then gave the impure phenansolved. The mixture was allowed to stand at room temthroline which was collected, washed with Water and perature for 16 hours, and was then poured into water dried Chromatography of a benzene Solution on an Sohd Whlch swarmed was filtered alumina column gave 1.9 g. of fairly pure 3,4,8-trimethylwashed wlth water, recrystalllzed from methanol, and 1,10 phenanthm1ine p 195 00 C 1 i ldehtlfied as 3 Y l' Sublimation under reduced pressure, followed by crystalmethylblltan-il-one 2- 66% y Obtalhed as P lization from benzene, gave pure 3,4,8-trimethyl-L10- lemon prisms, M.P. 73-74 C. Found: C, 74.5; H, 7.8; phenanthroline y N, 11.1; C H N O requires C, 74.8; H, 7.8; N, 10.9%.

The purified intermediate quino-lylamino ketone so pre- XA LES 4.7

pared can be cyclized to the equivalent 1,10-phenanthroline by heating in an arsenic acid reaction medium Preparation of di-, triand as indicated herein. tetramethyl-1,lO phenanthrolines (b) A solution containing the above-described intermediate quinolyla-rnino ketone, prepared on the same The [following general procedure was used: Each aminosoale and in the same way as described above but without quinoline Set in hhe table below was proceeding to the separation and purification steps, was d s olved in acet c acid 3 ml.) at -40 C., and the added over 0.5 hour to refluxing 80% arsenic acid (65% Corresponding tiff-unsaturated ketone ((1011 11101) was A5 0 25 ml.). The solution was refluxed for two hours, added. The mixture was left overnight, then added over then cooled and diluted with water (50 ml.), and insoluble 0.5 hour to refluxing 80% arsenic acid (10 ml.). The material was filtered off. Sodium hydroxide solution was 30 mixture was refluxed with stirring for a further three to then added to neutralize the excess of arsenic acid, and five hours, then diluted with an equal volume of water.

the precipitated 3,4,7,8-tetramethyl 1,10 phenanthroline Sodium hydroxide solution was added to a pH of 5.5, and was collected, washed with water and dried. The solid impurities were removed by filtration with the aid of was agitated with cold benzene ml.), filtered oh? and carbon. The solution was then basified and the phenandried, giving 10.3 g., M.P. 274-2 81 C. (76% of theory). throline filtered off, washed with water, dried and weighed.

Crystallization from methanol gave pure 3,4,7,8-tetra- 35 methyl-1,10-phenanthroline, M.P. 284 C. reduced pressure followed by crystallization from benzene (c) A mixture of 80% arsenic acid (117.5 g.) and 4- or methanol.

TABLE Example Aminoquinoline v Unsaturated Ketone Product Yield, m.p., percent C.

4 8-aminoquinoline Methyl isopropenyl ketone 3,4-dimethyl-1,IO-phenanthroline." 31 286 5 3,4-dimethyl-8-aminoquinoline Pent 3-en-2 one 2.4.7.8-tetramethyl-1,IO-phenanthroltne 88 200 6 2,4-dimethyl-8-amlnoquinoline Pent-3-en-2-one 2,4,7,9-tetramethyl-1,IO-phenanthrolme 78 201 7 3,4-dimethyl-8-aminoquinoltne Methyl vinyl ketone 3,4,7-trimethyl-l,10-phenanthrolme 52 221 hydroxy-Z-methyl butan-Z-one (35.5 g.) was stirred at EXAMPLE 8 o -70 Whlle dlmethyl's'ammoqumolme (50 Preparation of 3,4,7,8-tetramethyl-1,10-phenanthroline was added over 0.5 hour. At the end of the addition, the temperature was raised to 88 C. and stirring was con- 50 3i4-dlmethyl-s-am1n0q111n011ne Y Y- tinned for three hours at 88-90" C. Forty percent sodium methylbhtan-zonel afsenlc acld (80%, 10

Analytical samples were prepared by sublimation under hydroxide was then added gradually, with cooling, until and water were heated on a boiling water bath h h i h d a pH f g h i i d lid was for 4 /2 hours. The reaction mixture was cooled and then filtered, washed with water and dried. The solid was neutralized with 40% NaOH- After thh'fohgh washing triturated with toluene 140 ml.) at 25 0., then filtered 55 with hot Water, the product was dried and then extracted off and dried. The toluene-insoluble material was stirred with cold benzene I0 femo-ve benzene-501M915 impufities, at 25 C. for one hour with dilute acetic acid (20 g. in leaving l y LID-phenanthroline 380 ml. water), and insoluble material was filtered off. Repeating the above experiment wlth Sodium hydroxide solution was added to the filtrate until the arsenic acld P1115 water hfiing replaced y arsenic acid a slight precipitate was present; carbon (2 g.) was added, 60 (80%, 20 the Product was obtained in 52% of and the solution was filtered. The solution was heated to theoretical Y C. and basified with sodium hydroxide solution. The precipitated 3,4,7,8-tetramethyl-1,IO-phenanthroline was filtered ofl, washed with water and recrystallized from methanol, giving 42 g. (61% yield) and M.P. 280281 c. 65

EXAMPLE 9 Preparation of 3,4,7,8tetramethyl-1,10-phenanthroline 4-hydroxy-3-methylbutan-2-one (6.5 ml.) was added EXAMPLE 2 during 30 minutes to 3,4-dimethyl- 8-aminoquinoline (8.6 g.), anhydrous zinc chloride (6.8 g.) and arsenic Preparation of 3,4,7-trimethyl-1,-10-phenanthroline acid 15 at 90-100o Stirring and p ture were maintained for a further two hours, and the 4-methyl-8-aminoquinoline (0.498 g.) was treated with reaction mixture was then diluted with water (15 ml.) 4-hydroxy-3-methylbutan-2-one (0.4 g.) and arsenic acid and cooled to room temperature. The precipitated com (1.3 g.) under the conditions used in Example 1(c). The plex was collected and washed with a little cold water yield of 3,4,7 trimethyl 1,10 phenanthroline, M.P. and then boiled for five minutes with 40% NaOH (40 222-223 C., was 0.336 g. (48% yield). ml.). The precipitated phenanthroline base was collected,

7 drained at the pump, and recrystallized from methanol to give a product (56%), MP. 283284 C. No appreciable amount of product was obtained from the mother liquor of the complex.

EXAMPLE 10 Preparation of 3,4,7 ,8-tetramethyl-1,10-phenanthroline 4-hydroxy-3-methylbutan-2-one (6.5 ml.) was added to 3,4-dimethyl-8-aminoquinoline (8.6 g.) in arsenic acid (80%, ml.) and concentrated sulfuric acid (9 ml.). The addition lasted minutes, and during this time the reaction mixture was maintained at 115 C. by separating water from the refluxing liquid by a Dean and Stark head. After the addition was completed, stirring and temperature were maintained for a further two hours. The reaction mixture was cooled, diluted with water (25 ml.), and neutralized with NaOH. The product was purified in the usual way by benzene Wash, 5% acetic acid treatment, and recrystallization from methanol to give 3 ,4,7,8-tetramethyl-1,10-phenanthroline.

As employed herein with regard to the ,B-vinyl ketone and ,B-vinyl aldehydes, the term precursors connotes those materials which are readily converted to such ketones and aldehydes under aqueous acidic condition (e.g., upon treatment with mineral acid and water). The nature of said precursors, and their use in a Skraup-type reaction, is known to the art. In addition, said Skraup reaction, the starting aminoquinolines employed therein and the phenanthroline products which are recovered are all discussed at length in Organic Reactions, volume VII, chapter 2, pages 59-98 (John Wiley and Sons, Inc., 1953).

While the invention has been described herein with regard to certain specific embodiments, it is not so limited. It is to be understood that variations and modifications thereof may be made by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A process for the preparation of a 1,10-phenanthroline which comprises reacting a quinoline, having an unsubstituted 7-position, selected from the group consisting of (a) wherein D is selected from the group consisting of hydrogen, lower alkyl, phenyl, tolyl and xylyl, and n is an integer from zero to two, with a carbonyl component selected from the group consisting of (b) ,H-vinyl ketones of the formula,

wherein X and X are each selected from the group consisting of hydrogen and lower alkyl, and Q is selected from the group consisting of phenyl and lower alkyl, (c) ,B-vinyl aldehydes of the formula,

RCH=(|3 wherein R and R are each selected from the group consisting of hydrogen, lower alkyl and phenyl, and (d) the precursors of such ketones and aldehydes which are readily converted thereto under aqueous acidic conditions, the quinoline and the carbonyl component being heated, at a temperature of from about C. to about 130 C., in a reaction medium consisting essentially of arsenic acid.

2. A process as defined in claim 1 wherein the molar ratio of arsenic acid to quinoline is from about 1.521 to about 10: 1.

3. A process as defined in claim 1 wherein the carbonyl component is first added to a mixture of the quinoline and the arsenic acid at a temperature of from about 20 C. to about 40 C.

4. A process as defined in claim 1 wherein said carbonyl component is present in from 10% to 50% molar excess relative to said quinoline.

5. A process as defined in claim 4 wherein the molar ratio of arsenic acid to quinoline is about 2.5: l.

6. A process for the preparation of a 1,10-phenanthroline which comprises heating, at a temperature of from about 50 C. to about C., in a reaction medium consisting essentially of arsenic acid, a compound selected from the group consisting of ,B-quinolylamino aldehydes and ,B-quinolylamino ketones obtained by reacting, at a temperature of from about 20 C. to about 40 C., in the presence of a catalytic amount of a weak organic acid catalyst, a quinoline, having an unsubstituted 7-position, selected from the group consisting of (a) I IHz wherein D is selected from the group consistin of hydrogen, lower alkyl, phenyl, tolyl and xylyl, and n is an integer from zero to two, with a carbonyl component selected from the group consisting of (b) {3-vinyl ketones of the formula,

wherein X and X are each selected from the group consisting of hydrogen and lower alkyl, and Q is selected from the group consisting of phenyl and lower alkyl, (c) fl-vinyl aldehydes of the formula,

n-onrc-orro wherein R and R are each selected from the group consisting of hydrogen, lower alkyl and phenyl, and (d) the precursors of such ketones and aldehydes which are readily converted thereto under aqueous acidic conditions.

7. A process as defined in claim 6 wherein said weak organic acid catalyst is acetic acid.

8. A process as defined in claim 6 wherein the molar ratio of arsenic acid to quinoline in said reaction medium is from about 1.521 to about 10:1.

9. A process as defined in claim 6 wherein said carbonyl component is present from 10% to 50% molar excess relative to said quinoline.

References Cited UNITED STATES PATENTS 2,535,417 12/1950 Hodel 260-288 FOREIGN PATENTS 282,274 6/1952 Switzerland.

OTHER REFERENCES Elderfield Heterocyclic Compounds, vol. IV, Wiley, 1952 p. 21-4. QD400E4.

Case, J. An. Chem. Soc. vol. 70, 39946, 1948. QDlAS.

Willink, Rec. Tran. Chim., vol. 54, p. 282 (1935). 2D1R3.

ALEX MAZEL, Primary Examiner.

D. G. DAUS, Assistant Examiner.

U.S. Cl. X.R. 

1. A PROCESS FOR THE PREAPRATION OF A 1,10-PHENANTHROLINE WHICH COMPRISES REACTING A QUINOLINE, HAVING AN UNSUBSTITUTED 7-POSITION, SELECTED FROM THE GROUP CONSISTING OF (A)
 2. A PROCESS AS DEFINED IN CLAIM 1 WHEREIN THE MOLAR RATIO OF ARSENIC ACID TO QUINOLINE IS FROM ABOUT 1.5:1 TO ABOUT 10:1. 